The debate on the appropriate level of EU emission reductions for 2030 is being conducted in a scientific vacuum. Certainly the decision is ultimately political, but the neglect of any robust scientific framing is emblematic of how the rhetoric of climate change has come to dominate even well meaning discussions, whether amongst governments, NGOs, businesses or academics.

If the 2030 decarbonisation target is to align with the wording and spirit of the Copenhagen Accord, Cancun Agreement and the Camp David Declaration (May 2012), then it must be founded on transparent assumptions, including about the probability of 2°C, the choice of climate model and how the subsequent carbon budget should be apportioned.

As it stands, many of those undertaking internally consistent and quantitative analysis do so from a nebulous framing of these fundamental starting points. Consequently, whilst their recommendations may appease political sensibilities they are neither “consistent with science” nor on “the basis of equity”. This expedient framing of the EU 2030 target mirrors the UK’s similarly opportune choice of carbon budget. At the same time as the International Energy Agency reiterates how current emissions are in line with a “temperature increase of between 3.6 °C and 5.3 °C” (by 2100), analyses of the EU and UK’s fair contribution to 2°C typically refuse to offer candid and scientifically robust conclusions.

The evidence to the EAC reflects on the appropriate probability of 2°C, reframes deforestation emissions as a global overhead and, in line with international commitments, revisits the issues of equity and the apportionment of emissions.

It concludes that if the emissions of ‘less-developed’ nations (non-Annex 1) peak by 2025 and subsequently reduce at ~7% p.a., then for a ‘reasonable probability’ of 2°C the UK and EU must deliver immediate emission reductions of ~10% p.a., with complete decarbonisation of the energy system by around 2030. Such levels of mitigation are far beyond anything countenanced by those engaged in debates on the UK carbon budget or EU 2030 targets; yet if avoiding the 2°C characterisation of dangerous climate change is to be taken seriously, the maths of the situation are inescapable.

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Text from a submission to the parliamentary Environmental Audit Committee inquiry into the UK’s carbon budgets (May 2012 – used with permission and with small adjustments).

Considering the appropriate probability for 2°CFrom the Copenhagen Accord (2009) and subsequent COPs (conferences of the parties) through to the G8 Camp David Declaration (May 2012) the UK has repeatedly committed to making its fair contribution to “hold the increase in global temperature below 2°C, and take action to meet this objective consistent with science and on the basis of equity”. Moreover, much of the UK Government’s domestic language has, since its 2009 Low Carbon Transition Plan (DECC 2009), been around “must rise no more than 2°C” (p. 5, emphasis added). Whilst this qualitative language of consensus around 2°C has been clear and consistent for many years (“hold below”, “must not exceed”, etc.) there has been no open clarification as to what quantitative probabilities such language represents. Yet, without quantified probabilities it is not possible to determine the accompanying range of twenty-first century cumulative emissions budgets from which emission pathways can be derived (Anderson & Bows, 2008).

In the absence of any explicit quantification, probabilities may be inferred by adopting the approach developed for the IPCC’s reports, whereby a correlation is made between the language of likelihood and quantified probabilities (IPCC, 2010). Following this approach, the Accord’s, EU’s and UK Government’s statements all clearly imply very low (0%-10%) probabilities of exceeding 2°C. Even a highly conservative judgement would suggest the statements represent no more than a 33% chance of exceeding 2°C. However in 2013, and with the UK government’s preferred climate sensitivity and carbon cycle assumptions (Murphy et al 2004), a 0%-10% chance of exceeding 2°C would leave almost no available carbon budget. Stretching the probabilities much further really starts to detract from any reasonable interpretation of the “must not exceed” language; though given the emissions released since 2000, it is now difficult to envisage anything much lower than 30%-40% chance of exceeding 2°C being either physically viable or deliverable in practice.

Set against such a quantitative backdrop, DECC’s choice of a 63% chance of exceeding 2°C is clearly incompatible with the UK’s repeated commitments made at various international forums (Anderson et al., 2009). Consequently, the UK has at least (see below) two climate change targets. One with budgets related to “must not exceed” (say 0%-10% – and potentially 30%-40% chance of 2°C) and another with budgets related to a 63% chance of exceeding 2°C. These two budgets are associated with radically different emission pathways and hence provide fundamentally different criteria for judging the appropriateness or otherwise of alternative mitigation options – both individually and collectively.

Considering apportionment of the global carbon budget to the UKExacerbating the UK’s profoundly inconsistent domestic and international positions on climate change are issues related to how the UK chooses to apportion global emissions to the national level. In this regard two particular issues arise; a) who is responsible for deforestation emissions; and b) how should global emissions be divided between Annex 1 and non-Annex 1 nations. Both the issues relate to the equity dimension of mitigation and against which the UK’s current domestic position again conflicts with its international rhetoric.

Issue a) deforestation The UK’s budgets imply all responsibility for emissions from global deforestation accrue solely to those nations deforesting. Whilst, such a position may have merit in terms of increasing the available ‘energy’ budget to the Annex 1 nations such as the UK, it does so at the expense of major reductions in available ‘energy’ emissions space for the poorer, non-Annex 1, nations (where the deforestation is occurring). Climate change has arisen as an issue principally from the emissions of wealthier, and already deforested, Annex 1 nations (Anderson & Bows, 2011). It is therefore difficult, if not impossible, to reconcile the UK view that responsibility for current deforestation emissions belongs solely to those nations’ deforesting with the explicit equity dimension of various international agreements. In response to this inequity, deforestation could be considered as a global overhead, thereby allocating emissions from deforestation amongst all nations – not only those deforesting. Such a global overhead approach would not absolve non-Annex 1 nations of responsibility for deforestation emissions, as their available budget for energy-related emissions, along with the budget for Annex 1 nations, would still be reduced as a consequence of the emissions from deforestation. Anderson and Bows further defended this position by noting how historical emissions (pre-2000) are essentially considered a global overhead that favours Annex 1 nations. Ultimately they concluded that “getting an appropriate balance of responsibilities is a matter of judgment that inevitably will not satisfy all stakeholders and certainly will be open to challenge. As it stands, the approach… in which historical and deforestation emissions are taken to be global overheads, is a pragmatic decision that, if anything, errs in favour of the Annex 1 nations.”[1]

Translating this principle into a quantitative constraint for the UK, Anderson and Bows (2008) estimated a twenty-first century budget of 266GtCO2 from deforestation, which, disaggregated to the national level, equates to about a 20% reduction in the available energy-emission space in the UK’s budget. However, since Anderson and Bows first proposed the 266GtCO2 budget, deforestation emissions have fallen sharply, with a similar method likely to almost halve the global overhead to around ~150GtCO2.[2] In light of this, it is appropriate that the UK budget be reduced by approximately 7% to account for the nation’s ‘fair’ share of global deforestation.

Issueb) apportionment between nations A much more significant issue relates to assumptions about emissions from non-Annex 1 nations, and therefore what is a reasonable budget for Annex 1 nations, including the UK? As it stands the UK approach implies a highly inequitable division of emissions – with very little distinction drawn between the two groups. In brief, the UK choice of budgets and pathways is based on a global peak in emissions of around 2016, with non-Annex 1 nations, on average, peaking around 2 years later. As with the attribution of deforestation emissions, such a division of the global budget between Annex 1 and non-Annex 1 nations is far removed from both the wording and spirit of the equity dimensions of the various international climate change agreements.

Anderson and Bows (2011) took a different framing of equity than that assumed by the UK government (and the CCC 2008/10), starting instead with the question “what reduction profiles could non-Annex 1 nations reasonably be expected to achieve if pushed extremely hard in terms of a rapid transition away from their growing emissions and towards absolute mitigation”. They adopted a range of scenarios, but suffice to say the budget remaining for the Annex 1 nations in all of these was dramatically more challenging than the proportional budget adopted by the UK government.

In brief, and to put some perspective on the change in the scale of the challenge, if non-Annex 1 nations can peak by 2025, and reduce emissions thereafter at around 7% p.a. (approximately twice the level Stern et al suggest is possible with economic growth), then there is no discernible emission space remaining for Annex 1 nations. Only if the growth to a 2025 peak in non-Annex 1 emissions is radically curtailed to just 1% p.a. and subsequently reduced at over 7% from 2025, is there any space for Annex 1 emissions – but still only if the latter’s emissions begin reducing at over 10% p.a. immediately.

As Anderson and Bows (2011) demonstrates, the UK’s proportion of the global carbon budget for a 63% chance of exceeding 2°C is premised on an apportionment regime that is highly partisan and certainly far removed from the UK’s explicit and international commitments on equity.

Combining probabilities and equityFar from being a technical and nuanced issue, the disjuncture between the UK’s high profile and repeated commitments on 2°C and the Government’s legally binding carbon budgets is profound and with fundamental repercussions for the framing of carbon-reduction polices.

The legally binding budgets essentially reject 2°C in favour of maintaining some emission space out to 2050 and hence a relatively slow transition to a lower-carbon society. By contrast, taking Government international statements on 2°C as an honest reflection of commitments demands immediate behavioural adjustments alongside rapid penetration of low-carbon technologies; with complete decarbonisation of the energy system by 2030.

Ultimately, if the UK wants to develop a consistent and evidence-based framing of its climate change commitments, it needs to match its legally binding domestic budgets with its international rhetoric on 2°C.

[1] It is worth noting that, Jiankun, H et almake the case that “reasonable rights and interests should be strived for, based on the equity principle, reflected through cumulative emissions per capita”. Building on this ‘cumulative emissions per capita’ approach, the authors demonstrate how China’s historical cumulative emissions are only one-tenth of the average in industrial countries and one-twentieth that of the U.S.

[2] This is the subject of a paper currently being developed, and is again based on FAO and other similar data.